1. Field of the Invention
The present invention relates to a path changeover method and device, and in particular to a path or route changeover method and device used in an L2 network or the like applied with a link aggregation technology.
2. Description of the Related Art
FIG. 14 shows a configuration of an L2 network applied with a link aggregation technology generally known in the art. In this L2 network NW, between a transmission side switching device 1 and a reception side switching device 2 for a MAC frame FR a link aggregation LA logically integrating e.g. two physical paths P1 and P2 is provided, where relay devices 3_1 and 3_2 are provided in the path P1 as shown, and path lengths PL1 and PL2 of the paths P1 and P2 are mutually different (PL1>PL2 in the example shown).
The transmission side switching device 1 includes a transmission processor 10 for transmitting the MAC frame FR received from a client terminal (not shown) or the like at the former stage thereof to the path P1 or P2 through a transmitting port PT1 or PT2 respectively connected to the path P1 or P2.
The reception side switching device 2 includes a reception processor 20 for transmitting the MAC frame FR received from a receiving port PR1 or PR2 respectively connected to the path P1 or P2 to a client terminal (not shown) or the like at the latter stage thereof in the reception order.
In a normal operation where no transmission failure occurs in either the path P1 or P2, as shown in FIG. 15A a frame sender 11 included in the transmission processor 10 receives a MAC frame FR1 shown in FIG. 14.
At this time, the frame sender 11 extracts as address information AI a source MAC address SA=“x” and a destination MAC address DA =“y” stored in the MAC frame FR1 and gives them to a hash controller 12 together with trunk information (abbreviated as info in the Figures) TI=“trunk TR1” predetermined corresponding to a link aggregation LA (namely, the reception side switching device 2 forming a transfer destination of the MAC frame) shown in FIG. 14.
The hash controller 12 provides the trunk information TI to an LA table manager 13 to acquire port state information SI corresponding to the trunk TR1 from an LA table TBL3. The LA table manager 13 provides the port state information SI acquired to the hash controller 12.
It is to be noted that the above port state information SI indicates, as shown in the LA table TBL3, whether or not the transmitting port PT1 or PT2 is in an available state, where in the available state “IS: in service” is set while in the unavailable state “OOS: out of service” is set.
The hash controller 12 having received the port state information SI performs a predetermined hashing operation to the source MAC address SA=“x” and the destination MAC address DA=“y” in the address information AI and determines a transmitting port as a destination of the MAC frame FR1 based on the hashing operation result. If the destination of the MAC frame FR1 is determined to be the transmitting port PT1, the hash controller 12 provides a transmitting port notification NT indicating the transmitting port=“PT1” to the frame sender 11 since the transmitting port PT1 is now available (“IS: in service”).
It is to be noted that the MAC frame FR includes, as shown in FIG. 16, a VLAN tag TG and data DT or the like in addition to the above noted source MAC address SA and destination MAC address DA, so that the hash controller 12 can determine the destination of the MAC frame FR by performing a hashing operation to the VLAN tag TG or by performing a hashing operation only to one of the source MAC address SA and destination MAC address DA.
The frame sender 11 having been notified with transmitting port=“PT1” sends the MAC frame FR1 to the path P1 through the transmitting port PT1.
This enables the MAC frame FR1 to be received at a receiving port PR1 in the reception side switching device 2 after having passed through the relay devices 3_1 and 3_2 shown in FIG. 14, and transferred by a reception processor 20 to the latter stage.
Hereafter, unless a transmission failure occurs in the path P1, the transmission processor 10 transmits following MAC frames in which the source MAC address SA=“x” and the destination MAC address DA=“y” are stored, through the transmitting port PT1. Namely, a MAC frame having stored therein the same address information is to be transferred through the same path.
On the other hand, in a transmission failure FL occurring in the path P1, e.g. between the transmitting port PT1 and the relay device 3_1 as shown in FIG. 14, a transmission failure detector 14 forming the transmission processor 10 detects the transmission failure of the transmitting port PT1, and its notification NF is provided to the LA table manager 13, as shown in FIG. 15B.
The LA table manager 13 sets (updates) the port state information relating to the transmitting port PT1 in the LA table TBL3 to “OOS: out of service”.
When having received a MAC frame FR2 in which the source MAC address SA=“x” and the destination MAC address DA=“y” are stored, the frame sender 11 extracts, as shown in FIG. 15A, the source MAC address SA=“x” and the destination MAC address DA=“y” from the MAC frame FR2 as the address information AI, to be provided to the hash controller 12 together with the trunk information TI=“trunk TR1”.
Having acquired the port state information SI relating to the transmitting ports PT1 and PT2 from the MAC table TBL3 in the same manner as FIG. 15A, the hash controller 12 recognizes that the transmitting port PT1 which should be a destination of the MAC frame FR2 is in the unavailable state (“OOS: out of service”) and transmits a transmitting port notification NT indicating transmitting port=“PT2” instead of the transmitting port PT1 to the frame sender 11.
In response, the frame sender 11 judges that a transmission failure has occurred in the path P1 because the transmitting port which should be the destination is changed from PT1 to PT2 although the MAC frame FR2 in which the same source MAC address SA and destination MAC address DA as the MAC frame FR1 are stored has been received, so that the frame sender 11 transmits the MAC frame FR2 through the transmitting port PT2 to the path P2 after a predetermined changeover waiting time TW has lapsed.
It is to be noted that in the above noted changeover waiting time TW, a time sufficiently longer than a transmission delay time of the path P1 in comparison with the path P2 is set so that the MAC frame FR2 transmitted to the path P2 and MAC frames left in the path P1 may be maintained in the receiving order in the reception side switching device 2 (namely, the MAC frame FR2 may not arrive ahead of the MAC frames left in the path P1).
This makes the MAC frame FR2 received at the receiving port PR2 in the reception side switching device 2 in the normal order later than the MAC frames left in the path P1 and provided as an output by the reception processor 20 to the latter stage.
Thus, it is made possible for the transmission side switching device 1 and the reception side switching device 2 to guarantee the transfer order of the MAC frame between client terminals.
As a reference, there has been proposed a communication device for transferring MAC frames on an OC (Optical Carrier) line in an encapsulated shape (for example, see patent document 1).
Patent Document 1
Japanese patent application laid-open No. 2004-64574.
The above described prior art has a problem that since it changes over the destination port of a frame after a changeover waiting time has lapsed from an occurrence time of a transmission failure on the frame transmission side, the reception side has a blank time upon receiving the frame, causing a communication interruption (disconnection) over the network.